The amount of energy consumed by a load can be determined based on instantaneous power measurements for the load and the amount of time during which the power measurements were generated. Energy monitoring can be used to track the energy efficiency of components and/or facilities. For example, power usage effectiveness (PUE) is based on the energy efficiency of a computer data center that houses computer equipment. The PUE for a data center can be based on a ratio between the total amount of energy used by the data center and the amount of energy used by the computing components housed by the data center.